The present invention relates generally to the production of semiconductor devices and, more particularly, to methods for forming silicide plugs suitable for use in very large scale integrated semiconductor devices having large aspect ratios.
As the dimension of semiconductor devices are reduced to below deep-submicron, the contact hole of the semiconductor device becomes smaller. Increasing the degree of integration of the semiconductor device increases the aspect ratio of the contact hole of the device. When the contact hole having such an increased aspect ratio is subjected to a conventional sputtering process or a physical vapor deposition process, a large scale concave area or void is formed. Formation of a plug in the contact hole is one of the important sputtering processes used in producing deep-submicron semiconductor devices.
Recently, the process for forming contact plugs for achieving a multi-layer wiring has been valued in accordance with the increase of the aspect ratio of the contact hole. Conventional processes for via plugs are classified as follows. First, a tungsten plug is formed in the contact hole by vapor deposition of a CVD tungsten layer in the contact hole. Second, a poly plug is formed in the contact hole by vapor deposition of a polysilicon in the contact hole. Third, a selective silicide plug is formed in the contact hole.
There are two methods for forming the tungsten plug in the contact hole. While a blanket CVD tungsten layer is used in one method, a selective CVD tungsten layer is used in the other method.
Description of the conventional methods with reference to the drawing is given below for better understanding of the background of this invention. Referring initially to FIGS. 1A through ID, conventional contact plug formation processes using the blanket CVD tungsten layer are shown.
As shown FIG. 1A, on a starting material 11, such as a silicon substrate or a lower metal layer used in achieving a multi-layer wiring, an insulating film 12, such as an oxide film, is deposited and then subjected to a patterning process to form a contact hole 13. Next, as shown in FIG. 1B, an adhesive layer 14 selected from the group consisting of a Ti film, a TiW film, a TiN film and a Ti/TiN film is deposited on the entire resulting structure of FIG. 1A. Thereafter, as shown in FIG. 1C, a blanket CVD tungsten film 15 is deposited thick enough as to completely fill the contact hole 13. Finally, as shown in FIG. 1D, the blanket CVD tungsten film is subjected to an etch back process, so as to form a tungsten plug 16 in the contact hole 13.
Turning now to the method utilizing the selective CVD tungsten film to form the tungsten plug, the method comprises forming the contact hole as shown in FIG. 1A, to expose the starting material therethrough and selectively depositing a CVD tungsten film on the exposed starting material, to form a tungsten plug.
The blanket tungsten plug technology has disadvantages such as the occurrence of a void in the contact hole and the need for an adhesive layer due to the low adhesiveness. Also, the selective tungsten plug technology is disadvantageous in that special treatment is necessary for satisfying selective growth conditions since two contact holes having different depths are to be filled at the same time.
In order to form a poly plug in the contact hole, one of two methods, namely, a method using a blanket polysilicon film or a method using a selective polysilicon film, is used.
The method using the blanket polysilicon film to form the poly plug is similar to that using the blanket CVD tungsten film to form the tungsten plug as shown in FIG. 1. That is, the poly plug is formed by forming a contact hole on a starting material, depositing a polysilicon film doped with dopants on the entire surface consisting of the starting material and the contact hole, heat treating the polysilicon film and applying an etch back process to the treated polysilicon film.
This blanket poly plug technology can completely solve the problems generated in the technology for forming the blanket tungsten plug. For example, the blanket poly plug technology provides good coverage and conformity when depositing the polysilicon film and thus, is one of the most useful technologies in mass production. Nevertheless, the technology has the disadvantage that the poly plug formed has a large contact resistance.
Among the conventional processes for forming via plugs, a selective silicide plug is formed using either a selective epitaxy layer or a poly plug.
Referring now to FIGS. 2A through 2D, conventional silicide plug formation processes using the selective epitaxy layer are shown.
As shown in FIG. 2A, on a starting material 21, such as a silicon substrate or a lower metallic layer used in forming a multi-layer wiring, an insulating film 22, such as an oxide film, is deposited and is then subjected to a patterning process to form a contact hole 23. Next, a selective epitaxy layer 24 is grown in the contact hole 23 until it fills half of the contact hole 23 and then, a metal film 25, such as a cobalt film and a titanium film, is deposited on the entire resulting structure of FIG. 2A, as shown in FIG. 2B. Thereafter, a heat treatment is applied to the metal film 25, so as to form a silicide film 26, as shown in FIG. 2C. Finally, non-reacted metal film pieces are removed with an acid solution, so as to form a silicide plug 26' in the contact hole 23.
A silicide plug formation method using a poly plug has been well reported in IEEE Trans, Electron Devices 40.371, 1993. With reference to FIGS. 3A through 3H, conventional silicide plug formation processes using the poly plug are shown.
As shown in FIG. 3A, a field oxidation process is carried out on a silicon substrate 31 to form a field oxide film 32 thereon, and n-type impurities are implanted in the silicon substrate 31 to form an n.sup.+ type impurity region 33. Thereafter, a polysilicon film 35 is deposited on the entire resulting structure and then subjected to a patterning process so that polysilicon film 35 remains only on the field oxide film 32. An insulating film 34 is coated on the entire resulting structure and subsequently subjected to a patterning process, so as to form two contact holes 36 and 37, with the contact hole 36 on the polysilicon film 35 and the contact hole 37 on the predetermined portion of the n.sup.+ type impurity region 33, respectively. At this time, the two contact holes have different depths.
On the entire resulting structure of FIG. 3A, as shown in FIG. 3B, there is deposited a composite film 38 consisting of TiN and Ti having thicknesses of seventy nm and sixty rim, respectively. The TiN/Ti film 38 is heat treated at 600.degree. C. under nitrogen ambient. The resulting TiN/Ti film functions as an adhesive layer and a silicidation stopper.
As shown in FIG. 3C, a polysilicon film 39 without dopants is deposited on the entire resulting structure with a thickness of about one .mu.m with a low pressure CVD (hereinafter, "LPCVD") process, so as to completely fill the contact holes 36 and 37. Subsequently, an etch back process is applied to the polysilicon film 39 to expose the TiN/Ti film 38, leaving the polysilicon film 39 only in the contact holes 36 and 37, as shown in FIG. 3D. As a result, poly plugs 40 and 41 are formed in the contact holes 36 and 37, respectively. During the formation of the plugs, the TiN/Ti film 38 is not removed.
A nickel film 42 is then deposited on the entire resulting structure with a thickness of 500 nm using a sputtering process, as shown in FIG. 3E. A heat treatment is applied to the resulting structure of FIG. 3E at 600.degree. C. under an argon ambient, transforming the poly plugs 40 and 41 to nickel silicides (Ni.sub.3 Si) 43 and 44, respectively, as shown in FIG. 3F. Non-reacted nickel film 42 is selectively removed with 70% HNO.sub.3 solution, so as to form silicide plugs 43' and 44' in the contact holes 36 and 37, as shown in FIG. 3G. Finally, a metal wiring film (Al-Si-CuD.sub.5) 45 is formed on the entire resulting structure.
Since the TiN/Ti film 38 functions as a silicide stopper as mentioned above, two silicide plugs can be simultaneously formed in the two contact holes having different depths, respectively.
The physical properties of the metals required to form the silicide plug are as follows: since the formation processes for the plug are carried out after the formation of the source/drain region or the first layer wiring, first, the temperature of formation for metal silicide formation is to be low; second, metal atoms have to move when forming the silicide plug; third, the silicide plug is to be stable; and the specific resistance of the silicide plug is to be low.